There is a wide consensus that the world is moving toward a significant expansion in wind power generation. According to the U.S. Energy Information Administration (EIA), in 2010 wind energy accounted for about only 2% of the total electricity generated in the United States. Nonetheless, from the year 2000 to 2010, electricity generated from wind in the U.S. increased more than 15 fold. EIA reports that American wind power topped 4% of the total U.S. power capacity in 2013. Many believe that supplying 20% of our electricity from wind is within reach by 2030.
According to the U.S. Department of Energy, in order to harvest more energy at higher altitudes, where wind velocity is higher, wind towers are becoming taller. At the same time, in order to cut unit costs, wind turbines are gradually getting bigger and heavier and blades are getting longer. The Triangle Business Journal reported that “in 2000, wind turbines reached 80 meters with blades rotating, and by 2012, rotating blades reached heights of 130 meters. Allowing the height to grow beyond 180 meters could be a game changer.” The following considerations, therefore, are essential:
A major component of wind power project costs is invested in the fabrication, transportation, and installation of the support structure and foundations. Reducing costs of the superstructure and foundation systems, as well as facilitating the tower's installation and transportation to the project site, is necessary in making wind power more competitive with other sources of energy.
At the present time, the most common wind tower structure is a tapered-tube construction: a conical tower of a large diameter. It is a massive and costly structure. With the trend towards taller towers, larger and heavier turbines and longer blades, the diameter of today's tower will keep getting larger and its total cost rising steeply. Its fabrication, transportation, and erection costs will disproportionally increase, hindering the effectiveness of wind power installations and rendering the present tower structure less and less viable. Today, in some markets, wind is a competitive form of energy. The innovation proposed here resolves the shortcomings of today's tower and gives wind power a greater edge to become a mainstream energy resource in a wider marketplace.
According to a report by the United States Department of Energy (DOE) Plan for 2007-2012, taller wind turbine towers can access high velocity winds because of wind shear (an increase in wind velocity as height above the ground increases). However, taller towers are more expensive and more difficult to transport and erect. To support taller towers, turbine bases must normally grow in diameter. Bases that are more than approximately 4 meters in diameter cause transport costs to skyrocket because of limitations in road capacity, bridge heights, and utility line heights.
All wind towers installed to date, whether a tapered tube or a tapering lattice structure, are essentially the same basic structural system: a free-standing vertical cantilever. Lattice tower structures have been in use in transmission lines and antenna installations for many years. Some lattice towers, in one form or another, have been used in wind tower installations. At the present time, however, the most common wind tower structure is the tapered tube, a conical tower of a large diameter. It is a massive and costly structure. The base diameter of such a structure can exceed 4 meters when it gets taller than approximately 80 meters.
Tower structures are subjected to static and dynamic forces, primarily vertical forces, such as the self-weight of the tower, turbine, and blades, and to lateral forces, such as wind and seismic forces. Generally, however, the lateral forces drive the design of the wind towers. The lateral forces produce bending moments and sway the tower structure. As the tower gets taller and the turbine gets larger and heavier, the magnitude of the bending moments and sway increase considerably.
As today's free-standing tapered-tube tower structure becomes excessively large, it becomes prohibitively expensive, hindering the competitiveness of wind power as an alternative source of energy, thereby rendering such a structural system less and less viable. To prevent the costs of wind tower installations from spiraling out of control, there is a pressing need to reverse the limitations of the present tower system.